The present invention relates generally to recording and/or reproducing apparatus, and more particularly to apparatus in which audio signal is modulated upon a carrier whose frequency is switched from one frequency to another in response to a transducer head being switched from one track to the next and recorded on a common track with a video signal and upon playback a tracking control signal is derived from frequency-modulated crosstalk components detected from side tracks.
In helical scan type magnetic tape recording and reproducing apparatus, a pair of transducer heads are mounted at equal angular positions on the circumference of a rotary drum and a magnetic tape is looped around the drum over an arc of 180-degree and transported at a speed much lower than the circumferential speed of the rotary drum, and audio signal is recorded through stationary heads along one edge of the tape.
In video tape recording, the recent effort is toward recording as much video information as possible in as small a tape length as possible and lowering the tape transport speed. One disadvantage of the stationary head recording is that reduction in tape transport speed tends to degrade sound quality much more than it adversely affects on picture quality.
To overcome this problem, shared use of common tracks by video and sound signals has been developed. According to this method, baseband audio signal is modulated on a single carrier having a frequency differing from the frequency ranges of modulated video components. Because of the high rotational speed of the rotary drum, high quality sound recording is made possible even when the tape transport speed is lowered.
On the other hand, recent advances in tape recording material and in transducer heads have made possible high density video recording, which has enabled reduction of tape speed to such an extent that a single cassette tape for home video tape recorders can hold six-hour recordings. In such high density recording, signals are recorded on narrow, closely spaced apart tracks with no guard bands therebetween. A high degree of precision is thus required for controlling the transducer head to keep it in registry with desired track. This is particularly important for home video tape recorders where the tape drive mechanism is required to be as simple as possible to meet the objectives of low cost and ease of servicing. Difficulty has been encountered to ensure on-track registration when reproducing a material recorded on a different apparatus. The same applies to recorders of the type wherein special features are provided which include slow-motion, fast-motion and frame freeze reproduction. In such recorders use is made of a head moving mechanism which moves the head in a direction transverse to the length of track in response to an error signal representing the deviation of the head from the intended track.
To overcome this problem, one current approach involves the use of a pilot signal generator for generating pilot signals having different frequencies and recording the pilot signals on different tracks, and an envelope detector for detecting the envelope of the pilot signals to derive a tracking control signal therefrom. However, the pilot signal generator adds to the complexity and cost of the equipment and tends to interfere with desired signals.
Another approach is to record a frequency-modulated video signal and to oscillate the video head transeversely at a frequency 480 Hz during playback to cause variations in the FM signal to extract a tracking control signal from such variations. However, this approach still suffers from a drawback in that the FM signal variations appear at the output of a frequency demodulator as a noise.